The present invention relates to a method and plant for disinfecting a wooden container likely to have been contaminated by microorganisms during its use.
The envisioned field of application is especially, but not exclusively, that of sterilizing casks intended for aging wine or casks likely to contain foodstuffs.
Generally, wine ages in a cask for a period during which the components of the wine diffuse and react with the wood of the inner wall and the deeper layers of the cask. Next, the wine is removed and deposits may remain on the inner wall of the cask. For it to be used again, in a similar or identical application, the cask must be reconditioned, in order to remove any deposits, then disinfected.
The reconditioning consists in cleaning the inner walls of the cask and then in disinfecting it in order to obtain a satisfactory sanitary condition and optimum preservation of the casks.
Usually, the inside of the casks is disinfected or sterilized by the action of steam, which may be injected under pressure and held inside for a predetermined time. Thus, the heat energy destroys the microorganisms located in the cask. However, the destruction takes place with some time lag, given the thermal inertia of the cask walls, and hampers the efficiency of the method. In order to accelerate the disinfection rate, it is possible to increase the steam pressure in the cask, but this runs the not inconsiderable risk of explosion and/or increases the thoroughness with which the inner walls of the cask are washed.
Another drawback of sterilization by steam is that it contributes to swelling the wood which absorbs the water and makes it more malleable.
One object of the present invention is to propose a method of disinfecting wood likely to have been contaminated by microorganisms while avoiding the drawbacks connected with the use of steam.
To achieve this aim, according to the invention, the method of disinfecting a wooden container likely to have been contaminated by microorganisms is characterized in that said container is subjected to the action of an electromagnetic field, the frequency of which is between 1 MHz and 300 GHz, in order to destroy at least part of the population of microorganisms contained in said cask.
The action of the electromagnetic field throughout the frequency range from 1 MHz to 300 GHz produces oscillation of the polar molecules or of the ions which, by friction, causes heating of the material. Heat transfer by conduction plays a secondary role within the substance, unlike other heating techniques, but it equalizes the temperature locally.
The frequencies used have the advantage of involving radiation whose penetration is a few centimeters while penetration of the infrared radiation, the wavelength of which is between 10xe2x88x923 m and 10xe2x88x926 m and which is commonly used to heat material, is a few millimeters. Consequently, it is possible to cause heating of the inner surface of the wall, when it is a few centimeters thick, by friction of the polar molecules or of the clusters, virtually at any point and at the same time. In this way, the microorganisms attached to the inner surface of the container wall are destroyed by the action of the radiation, which makes it possible to increase the temperature of the environment of the microorganisms.
Preferably, the wooden container is a wooden cask intended to contain alcohols or foodstuffs. These casks consist of longitudinal wooden elements hermetically fastened to each other in order to form a container having cylindrical symmetry and retained by hoops which are usually metallic, the two ends of the container being closed by flat fonts [sic]. Although the presence of the metal hoops prevents it being possible to envision treating the casks with suitable electromagnetic radiation, which would cause electric arcs detrimental to the treatment and especially local heating likely to damage the wall, it turns out that the inner surface of the cask wall heats without electric arcs appearing at the metal hoops. Thus treating wooden casks by means of suitable electromagnetic radiation leads to optimum sterilization of its inner wall, on the one hand, which is in direct contact with the liquid which it is likely to contain, and of the whole cask, on the other hand. Although a cask is a closed container, the thickness of its wall being a few centimeters, the radiation produces an effect on its inner surface.
Apart from the direct action on the microorganisms, the radiation acts on their environment and, in particular, on the water which is inevitably present in relatively large quantities on or in the wall and which is a prime example of a polar molecule. The friction of the water molecules produces an increase in the temperature also contributing to degrading the microorganisms.
According to a preferred implementational mode, the frequency of the electromagnetic field is between 865 MHz and 5850 MHz, which corresponds to microwaves.
According to a particular feature, the wooden container can be moved with respect to an electromagnetic source so that the action of said field on said container is uniform. Thus the hot spots, separated by a half wavelength, which occur when an object is irradiated, are attenuated by conduction since the container can be moved with respect to the source.
According to another particular feature, the electromagnetic source can be moved with respect to said wooden container so as to be able to treat wooden containers which are fixed or too bulky to be transported, as is for example the case for vats and barrels, and to solve the problem of homogenizing the temperature within the container.
According to a third particular feature, an electromagnetic field of 2450 MHz plus or minus 25 MHz, the power output of which is greater than 5 kW, is applied for a time at least equal to 300 s for a standard container. Thus the amount of energy applied to the wooden container is enough to destroy at least part of the population of microorganisms contained in said cask.
Another object of the present invention is to supply a plant for sterilizing or for disinfecting at least one wooden container likely to have been contaminated by microorganisms during its use. The plant comprises treatment means in order to subject said container to the action of an electromagnetic field, the frequency of which is between 1 MHz and 300 GHz, so as to destroy at least part of the population of microorganisms contained in said cask.
Advantageously, the treatment means comprise at least one electromagnetic wave generator extended by an applicator which is connected thereto capable of making said waves interact with said wooden container. The applicator consists of a slot antenna forming a wave guide in order to make the waves interact accurately on the wooden container.
Preferably, the plant comprises a plurality of electromagnetic wave generators extended by waveguides which at least partially surround said wooden container. This arrangement makes it possible to treat the wooden container from several angles simultaneously and leads to a substantially uniform application over the surfaces of the container.
According to a particular characteristic of the invention, the plant comprises electromagnetic wave generators emitting waves whose frequency is between 1 MHz and 300 GHz and having a power output at least equal to 1 kW.
These features make it possible to destroy the microorganisms since the heat energy resulting from the action of the waves exceeds a value beyond which they cannot survive.
According to another particular feature, support means are provided located close to the waveguides and capable of supporting said wooden container.
Advantageously, the support means can be moved in order to displace said wooden container with respect to the waveguides so as to homogenize the action of the waves on said container and to treat the container uniformly.
According to a particular implementational mode, the treatment means can be moved with respect to said container for uniform treatment or so that they can be transported to the user site for fixed wooden containers.